Recreational alpine skiing, as it is taught and practiced around the world on groomed slopes, is a technique of controlled skidding. The modern ski is designed to skid on the snow in a manner that creates frictional forces that the skier uses to control both speed and direction. Often, a beginning skier is taught how to turn by manipulating pressure on the front and back of the ski unequally in order to create unequal skidding forces. It is the difference between front and back skidding forces that creates the turning moment. Virtually all recreational skiers make use of this basic technique.
The advent of ‘shaped’ or ‘parabolic’ skis has provided the alpine skier with an additional technique for turning: carving. Mastering the carved turn using these types of skis involves angulating the ski firmly onto one edge or the other—a technique that most beginning skiers find extremely difficult. The edge should lock into the snow and a specific arc or turn will occur automatically. The incredible control and efficiency of the ‘carved turn’ has made this technique highly desirable.
Unfortunately, pure carve skiing is difficult to attain as a practical matter. In his classic book “Skiing Mechanics,” and again in the 2001 edition “The New Skiing Mechanics,” John Howe states “There is only one true continuous, balanced, carved turn radius for a given side cut radius and velocity.” John Howe, The New Skiing Mechanics, p. 130 (McIntire Publishing 2d ed. 2001). In other words, the turning radius of a ski is ‘built into’ the ski through design and construction. Under specific conditions, the skier can only carve one turn radius. The skier is forced to change the conditions (e.g., change his or her speed) or break out of the carve and into a skid if a shorter or longer turn is desired.
This difficulty is exacerbated by the fact that the tip and tail of conventional skis are virtually unloaded before the ski is bent into a turn. It is not until the tip and tail edges have grabbed the snow and bent into an arc that the tip and tail of the ski apply significant pressure. Paradoxically, without this pressure, it is difficult to engage the edge to get the ski to bend in the first place. In order to initiate a subtle, long radius turn, the carving skier should be able to slightly roll the ski into a very gentle edge angle. In reality, current ski designs generally cannot respond to such subtle input because the tip and tail are unable to grab the snow effectively until they are bent into a more severe arc. These limitations generally confine the skier to a narrow range of turn radii, making continuous carve skiing problematic.
An alpine ski generally must have a running surface with edges to slide over and/or engage the snow, and sufficient longitudinal spring force to allow the ski to bend into an arc when angled, and then straighten out when placed flat. Historically, these two functions have been performed by a single component: a runner that acts as a long leaf spring and that has a polyethylene base to slide on the snow and steel edges to engage hardpack and ice. An alpine ski is thus basically a continuous leaf spring with a boot attached near the middle and the fore and aft extremities (tip and tail) cantilevered over the snow.
A conventional alpine ski has no preload forces on the tip and tail of the ski. (While the slight camber or arc designed into all conventional skis does create a very slight pressure at the tip and tail, it is negligible for purposes of steering the ski at shallow edge angles.) Thus, with the ski flat on a groomed snow surface, virtually all the weight of the skier is being applied to the snow directly under the skier's boot, with almost no pressure applied to the snow at the tip and tail of the ski. Unfortunately, it is the tip and tail of the ski that create stability and the most significant turning forces. This is a main reason why a conventional shaped ski tends to be unstable until it is edged to a significant angle, i.e., the characteristic turning arc of that ski. Additionally, the small area of high pressure under the boot causes the flat ski to go slower by penetrating the snow surface to a greater extent, which is undesirable for a ski racer.
Because conventional skis lack any significant preload in the straight or unbent condition, such skis are generally designed and constructed to function as a very high spring rate (very stiff) leaf spring. This high spring rate allows the tip and tail to build up significant pressure rapidly as the ski begins to bend, thus providing the required stability along the entire length of the ski at the characteristic turning radius. Unfortunately the high spring rate can also preclude any great variety of turning radii. Once the skier has used his weight to bend the ski into an arc against the high spring rate, the additional bending necessary to create a significantly tighter turning radius may not be possible for lighter skiers.
The high spring rate also tends to make the ski stiff and unforgiving over terrain that is not perfectly smooth, which can throw a recreational skier off balance.